In the fabrication of a composite article, it is typical to assemble a plurality of orientated dry fiber layers into a shape to match the shape of the article. This assembly of dry fiber layers is known as a "preform" which may subsequently be placed in a mold. Resin is then injected into the mold to infiltrate between the fibers, to fill out the composite part. This process for producing composite parts is known as "resin transfer molding" (RTM).
In such a process, it is difficult to incorporate a layer of unidirectional fibers, because there is no way to maintain dry unidirectional fibers in register during preform assembly. It is also difficult to place the fibers in a preform because of the tendency to separate. Even if one were to successfully place a layer of dry unidirectional fibers in the preform, it is likely that during resin injection, the fibers will separate and shift, thus reducing part strength, and making it difficult to maintain part to part consistency.
To overcome this problem, a preimpregnated unidirectional fiber tape was used which has a resin content of about 35% by weight. While sufficient to hold the fibers together, this tape failed to allow resin infiltration, and a boundary layer formed between the tape and the adjacent plys. This is unacceptable, as it provides a site for possible delamination and part failure. Consequently, the search continues for a unidirectional fiber tape which is drapable and handleable for adapting to the shape of the preform, provides sufficient cohesiveness to prevent fiber separation and additionally allows full resin infiltration during resin injection.